Diabetes is a group of diseases marked by high levels of blood glucose resulting from defects in insulin production, insulin action, or both. Diabetes can lead to serious health complications and premature death, but there are well-known products available for people with diabetes to help control the disease and lower the risk of complications.
Treatment options for people with diabetes include specialized diets, oral medications and/or insulin therapy. The primary goal for diabetes treatment is to control the patient's blood glucose (sugar) level in order to increase the chances of a complication-free life. It is not always easy, however, to achieve good diabetes management, while balancing other life demands and circumstances.
Currently, there are two principal modes of daily insulin therapy for the treatment of type 1 diabetes. The first mode includes syringes and insulin pens that require a needle stick at each injection, typically three to four times per day. These devices are simple to use and relatively low in cost. Another widely adopted and effective method of treatment for managing diabetes is the use of an insulin pump. Insulin pumps can help users keep their blood glucose levels within target ranges based on their individual needs, by providing continuous infusion of insulin at varying rates to more closely mimic the behavior of the pancreas. By using an insulin pump, users can match their insulin therapy to their lifestyles, rather than matching their lifestyles to how an insulin injection is working for them.
Conventional insulin pumps are capable of delivering rapid or short-acting insulin 24 hours a day through a cannula (typically a hollow metal needle or a flexible plastic catheter) placed under the skin. Insulin doses are typically administered at a basal rate and in a bolus dose. Basal insulin is delivered continuously over 24 hours, and strives to keep one's blood glucose levels in a consistent range between meals and overnight. Some insulin pumps are capable of programming the basal rate of insulin to vary according to the different times of the day and night. Bolus doses are typically administered when the user consumes a meal, and generally provide a single additional insulin injection to balance the carbohydrates consumed. Some conventional insulin pumps enable the user to program the volume of the bolus dose in accordance with the size or type of the meal consumed. Conventional insulin pumps also enable a user to infuse a correctional or supplemental bolus of insulin to compensate for a low blood glucose level at the time the user is calculating a meal bolus.
There are many advantages of conventional insulin pumps over other methods of diabetes treatment. Insulin pumps deliver insulin over time rather than in single injections and thus typically result in less variation within the blood glucose range that is recommended by the American Diabetes Association. Conventional insulin pumps may reduce the number of needle sticks which the patient must endure, and may make diabetes management easier and more effective for the user, to enhance the quality of the user's life. Typically, regardless of whether patients are on multiple direct injections (MDIs) or a pump, they take fasting blood glucose medication (FBGM) when they wake, and they also test for glucose in the blood during or after each meal to determine whether a correction dose is required. In addition, patients may test for glucose in the blood prior to sleeping to determine whether a correction dose is required, e.g. after intake of a snack.
There are generally two types of insulin pumps: conventional pumps and patch pumps.
Conventional pumps require the use of a disposable component, typically referred to as an infusion set, tubing set or pump set, which conveys the insulin from a reservoir within the pump into the skin of the user. An infusion set typically consists of a pump connector, a length of tubing, and a hub or base from which a hollow metal infusion needle or flexible plastic catheter extends. The base has an adhesive that retains the base on the skin surface during use. The base may be applied to the skin manually or with the aid of a manual or automatic insertion device. Often, the insertion device is a separate, stand-alone unit that the user is required to carry and provide.
Another type of insulin pump is a patch pump. Unlike a conventional infusion pump and infusion set combination, a patch pump is an integrated device that combines most or all of the fluidic components (including the fluid reservoir and pumping mechanism) in a single housing which is adhesively attached to an infusion site, and does not require the use of a separate infusion (tubing) set. A patch pump adheres to the skin, contains insulin (or other medication), and delivers the insulin over a period of time via an integrated subcutaneous cannula. Some patch pumps communicate with a separate controller device wirelessly (as in one device sold by Insulet Corporation under the brand name OmniPod®), while others are completely self-contained. These devices usually need to be replaced on a frequent basis, such as every three days, when the reservoir is exhausted or complications may otherwise occur.
An exemplary insulin patch pump 100 is shown in FIG. 1. The patch pump utilizes a single reservoir 110 that retains a full dose requirement for the duration of the pump device, which is typically 3 days. A pump engine 120 or other fluid driver typically applies force directly to the single reservoir 110, either through a secondary element, such as a plunger, or by direct deformation of the reservoir 110. This causes insulin to flow out of the reservoir 110 via the fluid line 112 and the cannula 111 and into the subcutaneous (SC) tissue of the patient.
In another type of patch pump 200, a simple form of a fluid driver is a preloaded spring 220, as shown in FIG. 2. In insulin patch pumps utilizing a preloaded spring 220, the continuous flow rate of insulin into the subcutaneous tissue is controlled only by a calibrated limiting orifice in the fluid line 212 or cannula 211, and the spring force applied to the reservoir 210 by the preloaded spring 220.
Shortcomings of this type of pump include spring force decay along the spring path resulting in flow rate decay, and spring force variation over the shelf life of the pump engine. Additionally, this type of insulin pump lacks a “fail-safe” or means of protecting the patient from accidentally receiving an entire reservoir volume or delivering the entire reservoir content.
Alternatively, in another type of patch pump 300, the flow rate of insulin into the subcutaneous tissue can be discontinuous by incorporating a directional control valve 330, such as an on/off valve, into the fluid line 312 to provide infusion via the cannula 311 when required, as shown in FIG. 3. However, the valve 330 when used with a fluid driver 320 could still fail in the open position, resulting in a single point failure which would allow the full dose of drug to be infused into the patient. For example, if the valve 330 shown in FIG. 3 fails, the fluid path remains open and the pressurized reservoir 310 will be completely infused into the patient.
FIG. 4 illustrates another patch pump 400 for the treatment of diabetes. The illustrated fluid driver is a pump engine or motor 420. This device is typically a stepper motor or other device that behaves similarly, such as a mechanism that advances a small incremental dose from a syringe-style reservoir 410 to the infusion site via the fluid line 412 and the cannula 411, as shown in FIG. 4. The illustrated device provides a superior form of insulin therapy as compared with Multiple Daily Injections (MDIs), which is the prevalent method of insulin therapy for both type 1 and type 2 diabetes. The current trend for basal delivery in the industry is to pump smaller incremental doses over the target duration and thereby approach continuous infusion. Smaller incremental doses are also more suitable for pediatric applications.
Dosing accuracy is still a concern with the current trend of pump engines. Applicable standards, such as IEC 60601-2-24, require dose accuracy to be within +/−5% of target, creating difficulty for conventional volumetric pumps, which push a plunger by extremely small linear translations, approximately 2 micrometers per step.
For injections, higher accuracy can be provided by reducing the syringe diameter so that the same linear translation of the syringe plunger provides a smaller dose. For example, the same incremental movement of the plunger in a 3/10 cc syringe 510 having an inner diameter D1 of 0.338 inch, as illustrated in FIG. 5A, provides one-eighth the dose for the same incremental movement as compared to a 3 ml syringe 520 or eight times the accuracy of a 3 ml syringe 520 having an inner diameter D2 of 0.110 inch, as illustrated in FIG. 5B. The higher accuracy of the 3/10 cc syringe 510 may eliminate or reduce dosing errors and enables the use of higher concentration drugs, such as U200 and U500 insulin, which is often prescribed for patients with type 2 diabetes.
Accordingly, there is a need for a fail-safe metering system for a fluid driver or pump engine that incorporates the improved dosing accuracy of a smaller syringe diameter and protects the patient from inadvertently receiving an overdose of medicament.
Additionally, there is a need for a low cost metering system that can operated with any fluid driver or pump engine, including a completely disposable pumping system such as a patch pump.